Linum is considered as the largest genus of Linaceae family, containing more than 180 species. The wide range of diversity within the genus Linum continues to challenge its taxonomical investigations. In present study anatomical features of vegetative organs, stem and leaf, of fourteen species, subspecies or varieties of three sections, were described with aim to improve the infrageneric classification of this genus. Plant samples were collected from natural populations of the studied taxa during 2011–2012. Embedded materials were used for microscopic investigation. Transverse hand sections of the lamina and stem were made from the middle part of fully-grown leaves and stems. Forty five qualitative and quantitative anatomical characteristics were examined in both stem and leaf. Principal Correspondence Analysis (PCA) of stem and leaf anatomical traits showed that some of these features were the most variable traits among the studied taxa. Analysis of variance showed significant differences for many of quantitative characteristics between taxons. A PCA biplot of anatomical features showed that some of the studied taxa had stable anatomical traits, which was confirmed by box and whisker plots. Cluster analysis of the studied taxa using the Unweighted Paired Group using Average method tree, as well as PCA and Principal Coordinate Analysis plots did not conform to the species classification in the traditional sections in references such as Flora Iranica and Flora of Iran and, with the exception of section Syllinum, the members of the other taxa did not occur together. Our results suggested that stem and leaf anatomical features were useful for infrageneric classification of the genus Linum.
